A large number of different radio frequency systems have come into use for communication, navigation, electronic warfare and radar systems. State of the art automotive and aerospaceborne vehicles which utilize such radio frequency systems could have more than a dozen separate antennas to cover a diversity of frequency bands. However, many mobile platforms have limited space for multiple antennas operating in widely separated frequency bands.
Alternatively, a number of wide bandwidth antenna elements have been developed for electronic warfare and signal intelligence systems. Current state-of-art antennas include flared notch elements each with about an octave of bandwidth (2:1). Other antenna elements such as spirals, log periodic elements, biconical dipoles and conical monopoles all have a bandwidth limit of about 2:1 and they tend to have relatively large physical dimensions, and, as such, are not well-suited for mobile platform/vehicular use.
One solution to this multi-antenna, multi-aperture problem now faced by land, sea, air and spaceborne vehicles has been multi-function, multi-frequency, phased array antenna apertures with electronic beam forming and scanning/tracking. However, today broadband antenna elements and phased array antennas are limited by the bandwidth and dimensions of the antenna feed elements to a maximum frequency ratio of about one octave (2:1). Broad bandwidth phased array antennas composed of broadband feed elements must address several conflicting design parameters:
1) low side lobes require that the phase centers of the feed antennas be closely spaced one half wavelength apart at the highest frequency of operation; PA1 2) feed antennas have dimensions approaching one half wavelength at the lowest operating frequency; PA1 3) large numbers of broadband amplifiers must be connected to every feed antenna in a 2:1 bandwidth array; and PA1 4) often a second set of crossed linear antenna elements and associated electronics are required if the array is to transmit and receive signals in orthogonal linear polarization and in both circular polarizations.
Therefore, there exists a need for an effective antenna structure which can cover a diversity of frequency bands, a diversity of polarizations, and can be useful in phased array antenna systems. The present invention provides a unique solution to meet such needs.